There has been known a structure using an electroluminescence (EL) element or an injection light-emitting diode in a current controlled light-emitting device used in a display device. Among other things, a current controlled EL (or a charge-injection EL, hereinafter referred to as organic light emitting element or organic EL) which uses an organic luminescence material as a light emitting layer is drawing attention as a display device which is high in luminance, large in size, low in manufacturing cost and capable of displaying full color images.
FIG. 7 is an enlarged schematic cross section of a principal part of a structural example of an organic light emitting element. For the sake of simplicity of description, FIG. 7 illustrates only a single pixel. The organic light emitting element ELD is provided with an anode AD formed of a transparent conductive thin film such as ITO on the inner face of a translucent glass substrate SUB and is configured such that a hole transport layer HTL and a luminescence layer LUL which are formed of thin film of an organic material and a cathode KD as a light emitting control electrode are sequentially stacked on the anode AD.
In the organic light emitting element ELD thus configured, a predetermined voltage is applied between the cathode KD and the anode AD to transport holes from the hole transport layer HTL to the luminescence layer LUL, causing the luminescence layer LUL to emit light, thereby emission light L is emitted from the glass substrate SUB. The above configuration is of a bottom emission type. For a top emission type, the emission light L is emitted to the side opposite to the glass substrate SUB.
FIG. 8 is an enlarged schematic cross section of a principal part of another structural example of an organic light emitting element. The organic light emitting element ELD is provided with an anode AD formed of a transparent conductive film (thin film) such as ITO on the inner face of a translucent glass substrate SUB which is the same as the above substrate, and is configured such that a hole transport layer HTL, a luminescence layer LUL and an electron injection layer EIL which are formed of a thin film of an organic material and a cathode KD are sequentially stacked on the anode AD.
In the organic light emitting element ELD thus configured, a predetermined voltage is applied between the cathode KD and the anode AD to transport holes from the hole transport layer HTL to the luminescence layer LUL and inject electrons from the electron injection layer EIL, causing the luminescence layer LUL to emit light, thereby emission light L is emitted from the glass substrate SUB.
The organic light emitting element ELD with the above stack configuration is provided with the hole transport layer HTL for injecting holes on the anode AD side and the electron injection layer EIL for injecting electrons on the cathode KD side to improve a light emitting efficiency.
FIG. 9 is a schematic cross section of a principal part of a conventional structural example of a top emission organic EL display device using the organic light emitting element ELD of this type. For the sake of simplicity of description, FIG. 9 illustrates only a single pixel to omit a switching element for selecting the pixel and a control element for controlling emission luminance.
As illustrated in FIG. 9, the organic EL display device using the organic light emitting element ELD is configured such that a sealing glass substrate SUB1 on the main surface of which the organic light emitting element ELD is formed is opposed to a translucent glass substrate SUB2 for protecting the organic light emitting element ELD and a sealing material SEA is applied to the periphery of both substrates and cured to bond both substrates together to isolate the inside from the outside, sealing the inside.
In general, a transparent drying material DES for controlling the degradation of the organic light emitting element ELD mainly due to humidity is fixed to the inner surface of the translucent glass substrate SUB2 (the surface opposing the main surface of the sealing glass substrate SUB1). The transparent drying material DES may be fixed by other methods: for example, a recess is formed in the inner surface of the translucent glass substrate SUB2 to bond the transparent drying material DES to the recess using an adhesive; or a glass cap GCP to which the transparent drying material DES is applied is bonded to the recess of the glass substrate. For the related art of the type described above, the following patent document 1 can be cited, for example.    Patent Document 1: Japanese Patent Application Laid-Open No. 2001-345175